Feeder control mechanism



Nov. 30, 1937. R. M. HARDGROVE FEEDER CONTROL MECHANI SM Filed April 5,1954 INVENTOR Pa/ph M Hat cl grove W ATTORN EY -Patented Nov. 30, 1937PATENT OFFICE 2,100,848 FEEDER CONTROL MECHANISM Ralph M. Hardgrove,Westfleld, N. 3., asslgnor to The Babcock 8a Wilcox Company, Newark N. Ja corporation of New Jersey Application April 3, 1934, Serial No.718,756

8 01a1ms.

The present invention relates in general to feeder control mechanisms,and more particularly to mechanisms oi this type for controlling thesupply of material to an endless bucket elevator. Such elevators areusually enclosed in a casing to confine the dusty atmosphere whichusually exists about the moving buckets and belt or chain upon whichtheyare mounted, and to return material spilled from the buckets to thebottom or boot of the elevator casing. The material to be elevated issupplied to the elevator casing boot where it is scooped up by themoving buckets as they pass about the lower chain sprocket wheel. As thebucketspass over the upper pulley of the elevatonthe material isdischarged by centrifugal force and gravity into an adjacent dischargechute. operation requires the supplying of material at a rate'substantially corresponding to the bucket capacity. When that rate isexceeded the height of material in the boot tends to increase, causingan increase in loadv on the elevator driving means, increased wear, andoverloading of the buckets with a resultant increase in the amountoiqnaterial spilled from the buckets. I have discovered that the airpressure conditions in, the

elevator casing tend to fluctuate with changes in the amount of materialspilled from the moving buckets and I advantageouslyemploy suchfluctuations in air pressure from a predetermined value to control theamount of material supplied to the elevator.

Elevators oi the above described type are used extensively in closedcircuit pulverizer systems to receive the discharge from a pulverizerand transfer the same to an elevated separator, from which theseparatedcoarse material is returned to the pulverizer and the finesdelivered to a storage system or point of use. .The raw material isnormally delivered to the-pulverizer by a regulable feeder mechanism,which, when a constant speed pulverizer driveis used, may be regulatedto vary'the amount of material passing through the pulverizer. Grindingconditions in the pulverizer maychange during operation, and cause thequality of the pulverized product to vary and the pulverizer drive motorto be overloaded or the', eleva'tor capacity to be exceeded. For/a givenmaterial having a deflhite'grindability, there is an optimum rate offeed and recirculation of material for the desired fineness.

The general object of my invention is the provision of an elevator ofthe character described with an improved system of controlling thesupply of material thereto. A further and more Economicalelevatorspecific object is the provision of an elevator feed controlsystem operable in response to fluctuations in air pressure in theelevator casing. A further specific objects the provision of a materialpulverizing system having provisions for controlling the supply ofmaterial to the pulverizer in response to the load on the pulverizerdrive mechanism and/or on an elevator of the type described receivingpulverized material from the pulverizer.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawing and descriptivematter in which I have illustrated and described a preferred embodimentof my invention.

0f the drawing:

Fig. 1 is a partly diagrammatic elevation 01' a closed-circuitpulverizer system incorporating my invention; and

Fig. 2 is a schematic diagram of the feeder control provisions. p v

In the closed-circuit grinding system illus trated in Fig. 1, rawmaterial is discharged from a feed bin ID to a suitable feeder ll drivenby a direct current shunt wound electric motor 82 in a well knownmanner. The raw'material is discharged by the feeder at a 'ratedependent on the speed of the motor l2 into a pipe l3 leading to apulverizer ll of the gravity-discharge type. The pulverizer ispreferably driven by a three phase constant speed electric motor l5 andthe pulverized material discharged through an inclinedconduit l6- intothe boot of a vertical elevator casing H. The casing l1 contains upperandlower sprocket wheels l8 and-.ldrespectively for driving an endlessbelt or chain 20 having a series of buckets 2i buckets are arranged topick up material in the casing boot during their passage therethroughand carry the same upwardly. As the buckets pass over theupper sprocketwheel, the material therein is discharged by gravity and centrifugalforce into a chute 22,which discharges into the upper end of a conical'air separator 23. The

' fine and coarse particles of material are separated therein, the finespassing through the pipe 24 to 'a pump or conveyor 25, having a ventpipe mounted thereon. The

26, and delivered to a storage system or point oi! use, while the coarseparticles or tailings are returned. to the pulverizer through a spout28. The

to the boot of the casing [1, then the amount of granular materialspilled in transit will correspondingly increase.

The elevator being of substantial height and the material conveyed of arelatively high density, the spilled material in falling exerts adragging effect on the air in the upper portion of the casing and causesthe air pressure in the lower part of the casing to build upcorrespondingly. I have discovered that the fluctuations in air pressurein the elevator casing bear a definite relation to the amount ofmaterial accumulated in the casing boot such that these fluctuations canbe used as a basis for controlling the pulverizer feeder motor l2.

It has been found desirable to employ'a constant speed motor l5 fordriving the pulverizer it. 'Any increase in supply of material to thepulverizer beyond the pulverizer capacity tends to overload the motor l5and adversely affect the fineness ratio, and a supplementary control mayadvantageously be employed in conjunction with the elevator casing airpressure responsive control, by which supplementary control the supplyof material may besuitably decreased whenever the motor l5'tends tobecome overloaded.

One form of suitable control system is illustrated in Fig. 2. The airpressure control may comprise a suitable pressure responsive device 30consisting of a liquid sealed floating bell- 3|, to the interior ofwhich is connected an air pipe 32, opening through one side of theelevator casing, as shown in Fig.' 1, slightly above the axis of thelower sprocket wheel I3 Above the bell 3| is mounted a counterweightedlever 33 pivoted at 34 and carrying a suitable mercury contact switch35, which is closed when the lever 33 is raised. A connecting member 36is mounted on the bell 3! for connecting the latter to and actuating thelever 33 on a change in air pressure in the elevator casing. Inoperation, the closing of switch 35 is used to short circuit a sector 31of a rheostat 38 in the field 39 of the feeder motor l2 to therebyeffect a predetermined decrease in the motor speed and consequently inthe amount of material delivered by the feeder H. The decrease in theamount of material delivered to the pulverizer causes a decrease in theamount of material supplied to the elevator casing. The air pressure inthe lower part of the casing consequently falls, causing the bell 3| todrop and the switch 35 to open, restoring the previous operatingconditions.

A corresponding controllingeifect on the feeder motor l2 may be effectedon a predetermined increase in the load on the pulverizer drive motor V15. For this purpose an overload relay 40 is inserted in the power linell to the pulverizer motor I5. On a predetermined increase in thecurrent through the relay, the contacts 42 and 43 I motor.

42 and 43 to open. A switch 44 is advantageously positioned in thecontrol system to permit the controls being thrown out of operation.

While the two parts of the control system operate independently, andeither may be used to the exclusion of the other, the simultaneous useof the two forms of control means has been found to be preferable, sothat the feeder is controlled not only in response to the load on thepulverizer drive motor IE, but also in response to the amount ofmaterial delivered to the elevator.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form of my invention now knownto me, those skilled in the art will understand that Cir changes maybemade in the form of the apparatus disclosed without departing from thespirit of the invention coveredby my claims, and that certain featuresof my invention may sometimes be used to advantage without acorresponding use of other features.

I claim:

1. In combination, an elevator casing having a material inlet at itslower end and a material outlet at its upper end, a feeder for supplyingmaterial to be delivered to said casing inlet, a motor for drivingsaidfeeder, an endless elevator having-substantially vertical runs insaidcasing and having a series of buckets thereon arranged to pick upmaterial in the lower end of said casing and discharge it at the upperend of said casing, and means responsive to fluctuations in the airpressure in said casing due to changes in the amount of falling materialtherein for controlling the operation of said feeder 2. In combination,an' elevator casing having a material inlet at its lower end and amaterial outlet at its upper end, a feeder for supplying material to bedelivered to said casing inlet, a motor for driving said feeder, anendless elevator having substantially vertical runs in said casing andhaving a series of buckets thereon arranged to pick up material in thelower end of said casing and discharge it at the upper end of saidcasing, an air conduit opening to said casing and responsive tofluctuations in air pressure insaid casing due to changes in theamountof falling material, an air pressure responsive deviceconnected tothe lower portion of said casing, and means actuated by said pressureresponsive device forcontrolling the operation of said feeder motor.

3. A grinding system including a pulverizer, a feeder for supplyingmaterial to said pulverizer, an elevator casing arranged to receive thedischarge of material by gravity from said pulverizer, endless bucketelevator means, in said casing, arranged to mechanically raise materialin said casing and means responsive to pressure changes in said casingfor controlling the. operation of'said feeder.

4. A grinding system including a pulverizer, a feeder for supplyingmaterial to said pulverizer, a substantially vertical elevator casingarranged to receive the discharge from said pulverizer, an endlessbucket elevator in said casing, and a device responsive to pressurechanges in said casing for controlling the speed of said feeder.

5. In a grinding system comprising a pulverizer, a drive motor therefor,a feeder for supplying material to said pulverizer, a drive motor forsaid feeder, an elevator casing arranged to receive the materialdischarged by'said pulverizer, and an endless elevator having oppositelymoving verti-"" cal ms in said casing and having a series of bucketsthereon arranged to pick up material in the lower end of said casing anddischarge said material at the upper end of said casing, means forcontrolling the operation of said feeder motor, and means responsive tochanges in the air pressure in Said casing for actuating said feedermotor control means.

6. In a grinding system comprising a pulverizer, a drive motor therefor,a feeder for supplying material to said pulverizer, a drive motor forsaid feeder, an elevator casing arranged to receive the materialdischarged by said pulverizer, and an endless elevator having oppositelymoving vertical runs in said casing and having a series of bucketsthereon arranged to pick up material in the lower end of said casing anddischarge said material in the upper end of said casing, means forcontrolling the operation of said feeder motor, means responsive tochanges in load on said pulverizer motor for actuating said feeder motorcontrol means, and means responsive to changes in the air pressure insaid casing for actuating said feeder motor control means.

7. In combination, a casing, an endless bucket elevator in said casing,means for supplying material to said casing to be raised therein by saidelevator, and means responsive to variations in the air pressure in saidcasing efiected by changes in the amount of material falling from saidelevator during operation for controlling the operation of said materialsupplying means.

8. In combination, a substantially vertical casing, means for supplyingmaterial to said casing, means for passing material through said casingand causing a variable supply of material to have a gravity drop in saidcasing, and means responsive to variations in the air pressure in thelower part of said casing effected by changes in the amount ofdescending material passing through said lower part of said casing forcontrolling the amount 0! material supplied to said casing. I

RALPH M. HARDGROVE.

